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What's the actual size of your 2" filters in "mm" with and without frame/ring? What step down adapter is suggested from a 52 mm to "-- mm"?

I am going to be shooting a full solar eclipse this summer. My thoughts are to use a 400mm Canon lens with a 2x converter. The barrel thread is 77mm what do you recommend?

24

Question by: Jens Lambert on Dec 28, 2016 9:00:00 PM | 1 Answer(s)

We would need the outer diameter of your lens to answer correctly. You will probably need an ASBF 70 or 80 filter.
Please check out our Baader Solar Filter Finder tool to make sure by yourself:http://astrosolar.com/baader-solar-filter/

What is the technical and visual difference between "Baader Double Polarizing Filter" and "Baader Single Polarizing Filter"?

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Question by: Roope Niemelä on Oct 26, 2017 9:26:00 AM | 1 Answer(s)

A single polarized filter is only polarizing the light in one direction. It can be used to dim light which is already polarized, like in a Herschel Wedge. Double polarizing filters are two single polarized filters in a row. When you turn one of them, you see that the light gets dimmed stageless from very bright to very dark. Double polarizing filters are mainly interesting for visual Moon observation. For high end / high resolution photographic use we recommend grey filters (ND filters)

Both thread sizes come with our proprietary pitch - which is not the same for the female and male threads.
This is our own proprietary "emergency solution" for uniting a world were manufacturers all over the world copy from each other - to the point that there are almost a dozen different pitches in use for male and female threads. Traditionally US-companies used to do a UNF-based pitch and the rest of the world went for metric threads - but these do vary from 0.5 to 0.75.

For this reason it does not make sense to publish our non standard pitch because our pitch is made to cope with all existing metric and US-pitch standards - and as said - our solution has evolved from sheer necessity. It is a mixture of a queer pitch and under-/over-dimensioning . We will not want to declare this as a standard and get bashed up for it. It works for us and is a result of 20 years adaptation to fit our filters onto all crazy threads we have seen. And inspite of this - every now and then there comes another "dragonboat-eyepiece" were even our filters may not fit...

Details

Baader Double Polarizing Filter

To screw into 1¼ or 2" eyepieces/threads. The two filters can be rotated against each other to always be able to achieve comfortable brightness level for moon observations, independent of moon phase. The Baader Double Polarizing Filter can also be used for solar observations in combination with an objective sun filter from Astro Solar Film.

The double polarizing filters in 1¼ or 2" can not be splitted into two parts, so you can't take one half as a single filter e.g. for a Herschel wedge. The reason for this is more stability and quality: If both housings could be separated, they may move or be tilted to each other, which could harm the image quality and cause reflexions.

Important Information for Observing the Sun

Polarizer and neutral density filters need additional filtering (for example, Herschel Prism or Astro Solar Safety Film) before the eyepiece of the telescope for observations of the sun. Using without the appropriate filters can cause damage to the these filters and eyesight.

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About Baader Filters
The variety of uses for filters in amateur astronomy has considerably increased during the last decade, enabled by both more accurately manufactured optical accessories, and, above all, by the “digital revolution“.
In the old days, colour filters for visual planetary observations were not screwed in the front part of the eyepiece, but were simply placed between the eyepiece and the eye. Plane-parallelism of these filter glasses was not important, because they were not in the optical path of the telescope.
Today, filters are placed in the optical path of the telescope, even well in front of the focal plane. This definitely requires some degree of plane parallelism and accurate production of the filter glasses.
Baader filter boxes can be attached laterally and above the other to create a sturdy unit. Each filter is then neatly in it's own drawer and characterised from the front with name, number and size of filter.
Every single cell mounted filter delivered to our customers is cut as a round or square disc in the according size (1¼", 31mm, 36mm, 2", 50,4mm, 50x50mm, 65x65mm), and then is polished plane to a quarter wavelength on both sides on a computer numerically controlled polisher. After that, the polished blanks are...

FAQ

Quite often we receive requests for a single filter in an off-standard size. In all cases we are sorry that we must answer as follows:

Sorry (we know it would be so very much cheaper in production - and we would be so much more flexible to fill special requests) - but we have decided long ago to not cut or saw our filters from large plates because this would leave the coating stack open and mutilated (with microscopic cracks) all around, prone to aging and peeling.

Many times we had the chance to inspect our competitors filters after several years of use (due to our 30+years of servicing SBIG-CCD-cameras/and filter wheels) and we realized already 15 years ago how moisture and heat stress can deteriorate even most modern hard coatings, slowly peeling off from the carrying substrate over time, unless the coating stack is sealed all around the filter stack.

As a consequence - in order to create our filters to remain impermeable - we only offer all filter substrates already cut to final shape and run each substrate on an double deck auto-polisher to achieve perfect optical flatness and freedom from cone errors.
Then we do individually coat these substrates in 500 pc per run as minimum to fill a complete coating chamber, in a way that the coating stack (many times 50+ layers) applied onto each filter won't reach to the very edge of the round or square substrate, so that the coating stack remains completely sealed from all sides. In this way we can ensure that our filters will not age at all.

The sad effect is that we cannot offer other sizes unless the inquired production quantity were in the range of 250 to 500 pc (depending on size) and the tooling rings or square holders will be paid for, which serve to precisely center each individual filter substrate within the rotating calotte inside the coating chamber. Sorry - as explained above - we just will not coat onto large plates and cut any shape from them, also because such large plates cannot be polished optically flat in the same way we do it.

For your most urgent need and for single piece solutions we can only recommend to order the next larger size of our respective filter and have that cut to shape by an ophtalmologist locally. We can supply the round filters without the metal cell in such cases; square filters come without cell in any case.

Unmounted Filters – which side should face the telescope?

Question in Detail:

I just bought LRGB 36mm unmounted filters. I have question: which side of filter should be placed towards telescope? Is it better way of distinguish than "more shiny surface towards telescope"?

Answer:

Always put the more reflective side towards the telescope side. To guide you we already put a small arrow on the filter rim, on those filters were the position matters. This arrow indicates which face of the filter should be directed towards the sky (telescope-sided). All cell-mounted filters are already oriented in a way that the most appropriate filter face is facing the sky when the filter would be mounted directly onto the front end of the nosepiece of a camera.
If you mount your filter the other way, any reflected light would have a short way to the camera sensor, resulting in a higher risk of getting some kind of back-reflections inside the camera field. Many sensors have highly reflective areas near to the light sensitive area, also the area with the bonding contacts is sometimes highly reflective.

But: this is true only for instruments without optical elements near to the focal plane. If you have f.e. a coma corrector, field flattener, focal reducer, focal extender (to a lower degree due to concave surface), or in extreme cases a whole lens group for more complex field corrections a few centimeters in front of the filter it could be useful to flip the filter against the rule from above (thus having the arrow pointing away from the telescope). Cause in such cases the likelihood of reflections from the sensor could be lesser then fort- and back- reflections from such glass-surfaces. If in doubt, it helps to make some test images from a star field with bright stars, using the filter in both ways for comparison.

Should you really have some reflections with both positions it can be more effective to add a spacer between filter and camera, eventually shifting the reflection out of the image field. With focal correctors having curved surfaces changing the filter-lens distance could help also.

Our company exists now for more than 50 years. In this time, more than 15.000 Baader Planetariums (the first patented product of our company) help all over the world to give students an understanding of astronomical correlations. In our own manufactory, more than 500 observatory domes have been produced and delivered turnkey-ready. Instruments and telescope accessories from "Baader" are known for their high qualities by many astronomers and universities. We consider it our duty and obligation, not only to sell telescopes, but an indivdually selected telescope system, that brings you a lifetime of joy.